JSDoc @template: Generics in return type of returned function is not evaluated.

[kennytm]

TypeScript Version: 2.2.2 (VSCode 1.11.1 on macOS 10.12.4)

Code

// JavaScript.
/**
 * @param {T} a
 * @returns {function(): T}
 * @template T
 */
function g(a) {
    return () => a;
}

let h = g(1)();

Expected behavior: The type of h is inferred as number.

Actual behavior: The type of h is inferred as T...?

[sandersn]

When we check whether a type parameter is in scope, the code currently only checks for Typescript type parameters, not for @template tags in the JSDoc. Since the compiler doesn't know T is in scope for instantiation, it just leaves it instead of mapping it to number. I'll have a fix up shortly.

[sandersn]

Fix is up at #16463